1. Field of the Invention
The present invention relates to a method of turbocharger control for use in automotive engine applications.
2. Description of Related Art
Supercharging is generally defined as the introduction of air, or an air/fuel mixture into an engine cylinder adding density greater than ambient. An increase in the density of the air/fuel mixture allows an increase in the amount of fuel in the cylinder and thus a greater potential power output. The primary objective of supercharging is to increase engine power output.
A turbocharger is a specific type of supercharger. A turbocharger consists primarily of a compressor and a turbine coupled on a common shaft. With a turbocharger, the exhaust gasses from the engine are directed in the turbine inlet casing to the blades of the turbine and are discharged through the turbine outlet to the exhaust pipe. The exhaust gasses are used in the turbine to drive the supercharging compressor which compresses ambient air and directs it into the intake manifold from which it enters the cylinders mixed with injected fuel.
A waste gate has been added to most conventional turbochargers in automotive applications, which allows the exhaust gas to bypass the turbine and go straight to the exhaust system. At higher engine speeds, the waste gate opens further to prevent overspeed and, subsequently, overboost. The waste gate allows gas to bypass the turbocharger, controlling maximum boost, maximum turbine speed and engine back pressure.
One disadvantage of the waste gate is that the energy contained in the exhaust gas passing through the waste gate is wasted. The gas bypasses the turbocharger and no useful work is obtained from it. A waste gate is therefore an inefficient method of controlling the turbocharger speed, boost and engine back pressure.
The turbine of a turbocharger develops power, or torque, by changing the angular momentum of the exhaust gasses. A conventional turbocharger typically uses a nozzle to increase this angular momentum. A nozzle directs the flow of the gas into the turbine wheel at an optimum angle for specific turbine speed at a specific flow.
A variable area turbocharger and variable nozzle turbocharger are typical types of variable geometry turbochargers which vary the size of the turbine inlet area. A variable nozzle turbocharger varies the inlet area to vary the exhaust gas inlet velocity and momentum.
It is a primary objective of the present invention to provide a method of controlling the angular position of vanes that form the turbocharger nozzle so as to maximize the available energy of the exhaust gas stream and apply that energy to the turbine wheel.